Capacitor discharge ignition system having circuit means for controlling the spark advance

ABSTRACT

A variable reluctance generator driven in synchronism with the engine produces electrical pulses which are coupled to a detector circuit that is responsive to the pulses reaching a given level to discharge the ignition capacitor to produce an ignition pulse. The generated pulses reach the given level in a timed relation to the engine r.p.m. in order to provide spark advance for the ignition system. A transistor is connected between the detector circuit and ground for shunting a portion of the generated pulses. Upon initial operation of the engine, a bias circuit connected to the control electrode of the transistor biases the transistor into conduction to shunt a portion of the pulses thereby reducing the sensitivity of the detector circuit so that the ignition timing remains constant during the initial operation. Subsequently, circuit biases the transistor out of conduction returning full sensitivity to the level detector for providing electronic spark advance.

United States Patent [72] Inventor William J. Warner Schaumburg, Ill. [211 App]. No. 852,313 [22] Filed Aug. 22, 1969 [45] Patented Apr. 6, 1971 [73] Assignee Motorola, Inc.

Franklin Park, Ill.

[54] CAPACITOR DISCHARGE IGNITION SYSTEM HAVING CIRCUIT MEANS FOR CONTROLLING THE SPARK ADVANCE 7 Claims, 1 Drawing Fig.

[52] US. Cl...; 3 l5/209CD, 123/117R, 315/209 SCR, 315/240 [51] Int. Cl F02p 5/08, I-IOSh 41/392 [50] Field of Search 315/209, 209 (CD), 209 (SCR), 209 (M), 241, 226, 214, 211,218,229; 123/117(R), 146.5, 148

[56] References Cited UNITED STATES PATENTS 2,852,590 9/1958 Fremon 123/148 3,240,198 3/1966 Loudon et al 123/148 Primary Examiner-Roy Lake Assistant Examiner--E. R. LaRoche Att0meyMueller, Aichele and Rauner ABSTRACT: A variable reluctance generator driven in synchronism with the engine produces electrical pulses which are coupled to a detector circuit that is responsive to the pulses reaching a given level to discharge the ignition capacitor to produce an ignition pulse. The generated pulses reach the given level in a timed relation to the engine rpm. in order to provide spark advance for the ignition system. A transistor is connected between the detector circuit and ground for shunting a portion of the generated pulses. lUpon initial operation of the engine, a bias circuit connected to the control electrode of the transistor biases the transistor into conduction to shunt a portion of the pulses thereby reducing the sensitivity of the detector circuit so that the ignition timing remains constant dur ing the initial operation. Subsequently, circuit biases the transistor out of conduction returning full sensitivity to the level detector for providing electronic spark advance.

Patented April 6, 1971 INVENTOR. WILLIAM J. WARNER BY 'h ww ATTORNEYS.

CAPAClTOllt lDlISlCll-llANGlE llGNllTllON SYSTEM lHlAVllNG lClllltC Ull'll MEANS lFOllt CONTlltOlLlLlNG 'llltlllE SlPAlltllfi ADVANCE BACKGROUND OF THE INVENTION Capacitor discharge ignition systems have been proposed wherein electronic spark advance is provided by driving a shaped segment at the r.p.m. of the engine past a variable reluctance coil thereby inducing pulses in the coil for operating a triggering circuit to discharge the ignition capacitor. However, for optimum starting it is desirable that the spark advance remain at zero degrees up to about 1,000 r.p.m. At that point, it is desirable for the spark to be advanced in proportion to increased engine r.p.m. One drawback in the past with the proposed electronic advance circuits is that the spark is advanced from the time the engine is first cranked, thereby making it more difficult to start the engine.

SUMMARY OF THE lNVENTlON lt is an object of this invention to provide an improved electronic advance circuit for a capacitor discharge ignition system.

it is a further object of this invention to provide an improved electronic advance circuit for a capacitor discharge ignition system that maintains the spark advance substantial! y at zero upon starting and until the engine reaches a predetermined r.p.m.

In one embodiment of this invention a variable reluctance generator is driven in synchronism with the engine for producing pulses which are connected to a level detector circuit, which is responsive to the pulses reaching a given level to discharge an ignition capacitor to produce an ignition pulse for operating the engine. A saturable oscillator is connected to the ignition capacitor for charging the same. The saturable oscillator includes a transformer having first and second inductively coupled windings wherein the first winding is connected to the output transistor of the oscillator and the second winding is connected to the control electrode of the output transistor so that increased current in the first winding due to conduction of the output transistor induces current in the second winding to sustain conduction of said transistor to saturation. When the transistor reaches saturation, the field collapses and induces a potential to charge the ignition capacitor. A bias circuit including first rectifier and a time base circuit is connected between the output transistor of the oscillator and the control electrode of a transistor connected between the level detector circuit and ground. The bias circuit also includes a second rectifier and time base circuit also connected between the output transistor and the control transistor. With conduction of the oscillator upon initial firing of the engine, the first rectifier applies a potential of one polarity to the time base circuit means charging the same thereby biasing the control transistor into conduction to shunt a portion of the generated pulses being applied to the level detector. In essence, this reduces the sensitivity of the level detector to a point where the ignition capacitor is discharged at the same time until the engine reaches a predetennined r.p.m. When the engine reaches a predetermined r.p.m., roughly 1,000 r.p.m., pulses of an opposite polarity coupled from the output transistor of the oscillator to the second time base means by the second rectifier charges the same to bias the control transistor out of conduction thereby returning the level detector circuit to full sensitivity so that spark advance is provided in direct relation to engine r.p.m.

DESCRllPTlON OF THE DRAWING The drawing is shown in a single FIGURE, which is a schematic diagram of a capacitor discharge ignition system in accordance with this invention.

DETAILED DESCRIlPTlON A capacitor discharge ignition system as illustrated in the drawing utilizes a generator driven in synchronism with the engine for producing electrical pulses to discharge the ignition capacitor. The generator includes a flywheel 110 which is driven in synchronism with the engine through a shaft l2, past the variable reluctance pickups 11A and 16. A shaped segment llltl mounted on the flywheel l0 generates a potential in pickups 11A and 16 substantially in the manner described in US. Pat. No. 3,356,896, assigned to the assignee of this application. The variable reluctance pickups M and 116 are connected to the gate electrodes l9 and 20 respectively of siliconcontrolled rectifiers (SCR) 22 and 24. Each SCR 22 and 2A acts as a level detector circuit for discharging the engine ignition capacitor 25. The parallel combination of capacitor 27 and thermistor 26 connected between the gates of each SCR and ground reference potential provide compensation for external noise and temperature variations.

As the level detectors 2A and 22 are gated on by the shaped segment llti moving past the variable reluctance pickups l6 and 11A, they discharge the capacitor through the SCR 22, for instance, which potential is inductively coupled by transformer 52 to the gate 5A of the SCR 336 to discharge the ignition capacitor 25 through the SCR 36 and the ignition coil A0. This generates a spark across the gap A2 to fire the engine. Similarly, the triggering of SCR 2A discharges the capacitor 30 through the transformer A5 to trigger SCR A7 thereby discharging the ignition capacitor 25 through the ignition coil 50 to provide a spark across the gap 52. The diodes 5A and 56 across the respective ignition coils 50 and A0 act to suppress negative transients generated by the collapsing fields in the coils.

A saturable oscillator 60 is used to charge the ignition capacitor 25 upon the discharge thereof through the ignition coils. The oscillator includes a first winding 62 that is connected to the emitter or output electrode 6A of oscillator output transistor 65. A second winding 66 is inductively coupled to the winding 62 and is connected through the parallel combination of diode 66 and resistor 69 and resistor 70 in series therewith to the base or control electrode 72 of the transistor 65. A Zener diode 7A connected between the collector electrode 75 and the base electrode 72 of transistor protects the transistor from overvoltage.

0n initial operation, the shaped segment lltl of flywheel l0 induces a voltage in variable reluctance pickup 116, for instance, to trigger SCR 2A thereby gating on SCR A7. With SClR A7 conducting a potential filteredl by capacitor S2 is coupled by diode S0 to the collector electrode SA of transistor 65 through the collector biasing resistor 67. Because the base electrode SS of transistor 65 is grounded through resistor 69, diode S0, SCR A7 and the ignition coil 50, the transistor S5 conducts applying a potential through diode 92 and resistor to the control electrode 72 of transistor 65. This drives transistor 65 into conduction through the first coil 62 of the saturation oscillator. Since the coil 62 is inductively coupled to coil 66, the potential is fed back by resistor 70 to the base 72 of the transistor 65 to maintain that transistor in conduction to saturation. When the transistor reaches saturation, the

field of the transformer collapses inducing a potential in coil 55 that is coupled by resistor 96 to charge the ignition capacitor 25.

it can be seen that as the engine commences to run the shaped segment i8 is driven past the variable reluctance pickups 116 and 11A in an ever increasing rate of speed thereby causing a potential to be induced in the variable reluctance pickups which reach the level required to trigger the SCRs 2A and 22 at a point of time which decreases directly with engine r.p.m. thereby providing spark advance. However, it is desirable in some internal combustion engines that the spark advance remain substantially at zero until the engine reaches about 1,000 r.p.m. for ease of starting. in order to provide a constant zero advance from starting until the engine reaches 1,000 r.p.m., l have designed a unique circuit. Essentially, the circuit for controlling the spark advance includes an electron control device or transistor 100, the collector 102 of which is connected through the diodes 104 and 106 to the gates 19 and 20 respectively of each SCR or level detector 22 and 24. The emitter electrode 108 is connected to a ground reference potential. A biasing circuit 110 is connected between the output electrode 64 of transistor 65 and the control electrode 112 of transistor 100. The biasing circuit 110 has a first portion comprising a rectifying diode 114 and a time base circuit, comprising resistor 115 and capacitor 116, which is connected by thermistor 118 to the control electrode 112 of transistor 100. The biasing circuit 110 also includes a second portion comprising rectifying diode 120 and a time base circuit, comprising resistor 121 and capacitor 122, which is also connected to the control electrode 112 of transistor 100 by resistor 123.

In operation, when the engine is first started, the positive portion 124 of the alternating current 125, which is present on the emitter electrode 64 of the oscillator output transistor 65 during operation of the oscillator, is connected through the diode 114 and charges the capacitor 116, the potential on which is connected to the base 112 of the transistor 100. This biases the transistor 100 into conduction effectively shunting a portion of the pulses from the variable reluctance pickups 14 and 16 through the transistor 100 to ground. This reduces the sensitivity of each SCR 22 and 24 such that they are gated on at the same time for each revolution of the flywheel irrespective of the rate of rotation of the same until the flywheel reaches a predetermined r.p.m., which is in the proximity of 1,000. At this point, because the time constant of the time base circuit of the second portion of the bias circuit 110 is greater than the first portion, as is the potential that capacitor 122 can hold, the negative swing 127 of the wave 125 charges the capacitor 122 to a point that the potential thereon coupled through resistor 123 biases the transistor 100 out of conduction. With the transistor 100 biased out of conduction, each SCR 22 and 24 returns to full sensitivity thereby providing electronic spark advance in direct proportion to the engine r.p.m.

Although these FlGS. are not meant to limit this invention in any manner in one working embodiment of the ignition circuit it was found that the following values of the bias circuit 110 were satisfactory.

Resistor 1153.3K ohms Thermistor 118-150K ohms Capacitor 1161.0 pfd. Resistor 1214.7K

Resistor 123-100K Capactor 122.1 .rfd.

What has been described, therefore, is a unique electronic spark advance circuit for a capacitor discharge ignition system that maintains the spark advance constant upon starting until the engine reaches a predetermined r.p.m. at which time the spark is advanced in proportion to the increased engine speed.

1 claim:

1. In a capacitor discharge ignition system for an internal combustion engine having generator means driven in synchronism with the engine for producing electrical pulses, and detector means responsive to the pulses reaching a given level to discharge the ignition capacitor to produce an ignition pulse for operating the engine, the generated pulses reaching the given level in a time relation to the engine r.p.m. to provide spark advance, the combination including, control circuit means connected to the detector means, first circuit means connected to said control circuit means for operating the same to a first condition for reducing the sensitivity of the detector means during the initial period from engine starting until the engine speed reaches a predetermined r.p.m. thereby maintaining a substantially constant means rate of spark advance during said period, and second circuit means connected to said control circuit means and being responsive to the engine speed exceeding said predetermined r.p.m. to operate said control circuit means to a second condition to render substantially full sensitivity to the detector means so the generated pulses reach the given level in a timed relation to the r.p.m. thereby providing spark advance.

2. The capacitor discharge ignition system of claim 1 wherein said control circuit means is an electron control device connected between the detector means and said first and second circuit means, said first and second circuit means each applying a bias potential to said electron control means in response to the engine r.p.m. to control the electron flow therethrough thereby controlling the sensitivity of the detector means.

3. The capacitor discharge ignition system of claim 1 wherein said control circuit means is a transistor having a control electrode, said transistor being connected between the detector means and a reference potential, said first circuit means comprising a first time base circuit including a capacitor connected to the control electrode of said transistor, said capacitor being charged in response to a potential during said initial period of engine operation to bias said transistor into conduction thereby shunting a portion of the generated pulses to reduce the sensitivity of the detector means, and said second circuit means comprising a second time base circuit including a second capacitor connected to the control electrode of said transistor, said second capacitor being charged at an engine r.p.m. greater than said predetermined r.p.m. to bias said control transistor out of conduction thereby returning substantially full sensitivity to the detector means.

4. A capacitor discharge ignition system for an internal combustion engine, including in combination, generator means driven in synchronism with the engine for producing electric pulses, level detector circuit means coupled to said generator means and being responsive to the generated pulses reaching a given level to discharge the ignition capacitor to produce an ignition pulse, saturable oscillator means coupled to the ignition capacitor for charging the same, said oscillator means comprising a transistor having control and output electrodes and a transformer having first and second inductively coupled windings, said output electrode of said transistor being coupled to said first winding, and circuit means for connecting said second winding to said control electrode of said transistor so that increased current in said first winding due to the conduction of said transistor induces current in said second winding to sustain conduction of said transistor into saturation, control circuit means connected to said level detector circuit means, and bias circuit means having first and second portions connected between said output transistor of said saturable oscillator means and said control circuit means, whereby conduction of said saturable oscillator means with initial operation of the engine energizes said first portion of said bias circuit means through said output transistor to bias said control circuit means to a first condition thereby shunting a portion of the generated pulses required to discharge the ignition capacitor to effectively maintain the spark advance constant during the initial operation of the engine, and said second portion of said bias circuit means being responsive to the conduction of said output transistor with the engine r.p.m. reaching a predetermined amount to bias said control circuit means to a second condition to provide spark advance relative to engine r.p.m.

5. The capacitor discharge ignition circuit of claim 4 wherein said level detector circuit means includes a siliconcontrolled rectifier having a gate electrode, said generator means being connected between said gate electrode and a reference potential, said control circuit means includes a transistor having a control electrode and being connected between said gate electrode and a reference potential, and

said first and second portions of said bias circuit means are connected to saidcontrol electrode, said first circuit portion acting to bias said transistor into conduction to shunt a portion of the generated pulses to the reference potential, and said rectifier and second time base circuit means connected between the output transistor of said saturable oscillator and the control electrode of said control transistor, said second rectifier coupling pulses of a polarity opposite said one polarity to said second time base circuit means to charge the same to render said control transistor nonconductive.

7. The capacitor discharge ignition system of claim 6 wherein said second time base circuit means has a greater time constant than said first time base circuit means. 

1. In a capacitor discharge ignition system for an internal combustion engine having generator means driven in synchronism with the engine for producing electrical pulses, and detector means responsive to the pulses reaching a given level to discharge the ignition capacitor to produce an ignition pulse for operating the engine, the generated pulses reaching the given level in a time relation to the engine r.p.m. to provide spark advance, the combination including, control circuit means connected to the detector means, first circuit means connected to said control circuit means for operating the same to a first condition for reducing the sensitivity of the detector means during the initial period from engine starting until the engine speed reaches a predetermined r.p.m. thereby maintaining a substantially constant means rate of spark advance during said period, and second circuit means connected to said control circuit means and being responsive to the engine speed exceeding said predetermined r.p.m. to operate said control circuit means to a second condition to render substantially full sensitivity to the detector means so the generated pulses reach the given level in a timed relation to the r.p.m. thereby providing spark advance.
 2. The capacitor discharge ignition system of claim 1 wherein said control circuit means is an electron control device connected between the detector means and said first and second circuit means, said first and second circuit means each applying a bias potential to said electron control means in response to the engine r.p.m. to control the electron flow therethrough thereby controlling the sensitivity of the detector means.
 3. The capacitor discharge ignition system of claim 1 wherein said control circuit means is a transistor having a control electrode, said transistor being connected between the detector means and a reference potential, said first circuit means comprising a first time base circuit including a capacitor connected to the control electrode of said transistor, said capacitor being charged in response to a potential during said initial period of engine operation to bias said transistor into conduction thereby shunting a portion of the generated pulses to reduce the sensitivity of the detector means, and said second circuit means comprising a second time base circuit including a second capacitor connected to the control electrode of said transistor, said second capacitor being charged at an engine r.p.m. greater than said predetermined r.p.m. to bias said control transistor out of conduction thereby returning substantially full sensitivity to the detector means.
 4. A capacitor discharge ignition system for an internal combustion engine, including in combination, generator means driven in synchronism with the engine for producing electric pulses, level detector circuit means coupled to said generator means and being responsive to the generated pulses reaching a given level to discharge the ignition capacitor to produce an ignition pulse, saturable oscillator means coupled to the ignition capacitor for charging the same, said oscillator means comprising a transistor having control and output electrodes and a transformer having first and second inductively coupled windings, said output electrode of said transistor being coupled to said first winding, and circuit means for connecting said second winding to said control electrode of said transistor so that increased current in said first winding due to the conduction of sAid transistor induces current in said second winding to sustain conduction of said transistor into saturation, control circuit means connected to said level detector circuit means, and bias circuit means having first and second portions connected between said output transistor of said saturable oscillator means and said control circuit means, whereby conduction of said saturable oscillator means with initial operation of the engine energizes said first portion of said bias circuit means through said output transistor to bias said control circuit means to a first condition thereby shunting a portion of the generated pulses required to discharge the ignition capacitor to effectively maintain the spark advance constant during the initial operation of the engine, and said second portion of said bias circuit means being responsive to the conduction of said output transistor with the engine r.p.m. reaching a predetermined amount to bias said control circuit means to a second condition to provide spark advance relative to engine r.p.m.
 5. The capacitor discharge ignition circuit of claim 4 wherein said level detector circuit means includes a silicon-controlled rectifier having a gate electrode, said generator means being connected between said gate electrode and a reference potential, said control circuit means includes a transistor having a control electrode and being connected between said gate electrode and a reference potential, and said first and second portions of said bias circuit means are connected to said control electrode, said first circuit portion acting to bias said transistor into conduction to shunt a portion of the generated pulses to the reference potential, and said second circuit portion of said bias circuit means acting to bias said transistor out of conduction.
 6. The capacitor discharge ignition system of claim 5 wherein said first portion of said bias circuit means includes a rectifier and time base circuit means connected between said output transistor of said saturable oscillator and the control electrode of said control transistor, said rectifier coupling pulses of one polarity to said time base circuit means to charge the same to render said control transistor conductive, and said second portion of said bias circuit means includes a second rectifier and second time base circuit means connected between the output transistor of said saturable oscillator and the control electrode of said control transistor, said second rectifier coupling pulses of a polarity opposite said one polarity to said second time base circuit means to charge the same to render said control transistor nonconductive.
 7. The capacitor discharge ignition system of claim 6 wherein said second time base circuit means has a greater time constant than said first time base circuit means. 